The present invention relates to an aptamer which binds to protein A, G or L, substances comprising protein A, G or L or microorganisms comprising protein A, G or L, in particular Staphylococcus aureus, Streptococcus or Peptostreptococcus, uses of the aptamer and methods for the detection and enrichment of protein A, G or L, substances comprising protein A, G or L or microorganisms comprising protein A, G or L in which the aptamer is employed.
Staphylococcus aureus is a spherical, Gram-positive, pathogenic bacterium. S. aureus occurs almost everywhere in nature, including on the skin and in the upper respiratory passages of 25 to 30% of all humans. Antibiotic-resistant forms and especially multiresistant forms are particularly hazardous. These occur to an increased extent in hospitals, care homes, and also in sewerage sludge. Resistant germs of the strain are also found in foodstuffs of animal origin. The germ can also enter into drinking water. Frequent diseases which are to be attributed to S. aureus are sepsis, skin and wound infections, pneumonias, abscesses, furuncles, endocarditis, osteomyelitis, food poisonings by S. aureus exotoxins and mastitis in cattle.
The detection of S. aureus has hitherto been carried out by means of cultivation or immunological and molecular biology methods (antibody assays, PCR-based methods). The methods are either time-consuming or expensive. The object of the present invention was therefore to provide specific substances which render possible a rapid, simple and reliable detection of S. aureus. 
The object is achieved with an aptamer which binds to immunoglobulin-binding cell wall proteins, to substances which comprise an immunoglobulin-binding cell wall protein and to microorganisms which comprise an immunoglobulin-binding cell wall protein, wherein the immunoglobulin-binding cell wall protein is chosen from the group including or consisting of protein A, G or L.
In the context of the above paragraph, the term “including” means that the aptamer can also bind to further immunoglobulin-binding cell wall proteins, or to substances or microorganisms which comprise an immunoglobulin-binding cell wall protein other than the proteins A, G or L mentioned.